Gibbon Systematics and Species Identific- Ation’ Is One Which I Am Particularly Pleased and Proud to Be Able to Publish

1 International Zoo News Vol. 42/8 (No. 265) December 1995 Cover Illustration: Adult female Javan gibbon (Hylobates moloch), Paignton Zoo, England, 22 October 1988. Notice the sharp white brow band and the distinct white goatee beard typical of this species, and the black cap which is often more prominent in females than in males. (Photo: Thomas Geissmann) 2 International Zoo News Vol. 42, No. 8 (1995), p. 466 EDITORIAL This issue ofl.Z.N. is atypical in two respects – it is dominated by a single, unusually long, feature article (which includes four pages of colour plates), and it contains, for the first time in the magazine’s history, indexes to the contents of the current volume. Thomas Geissmann’s article ‘Gibbon systematics and species identification’ is one which I am particularly pleased and proud to be able to publish. A good all-round zoologist, perhaps, should not have favourite species; but the gibbons have had a special place in my affections ever since I first marvelled at them as a child at London Zoo. Their beauty, their agility and grace, the haunting magic of their songs, even (to anthropomorphise for a moment) their gentleness and exemplary family life, seem to give them a unique appeal. Today, of course, like every animal whose sole habitat is the South-east Asian rainforests, gibbons are under threat. More than ten years ago, only five of their taxa were reported to be ‘relatively safe’ in at least some part of their ranges, and the situation is unlikely to have improved since then. Ultimately, habitat protection is probably their only hope, but ex situ breeding can help in some cases. And for this, reliable species identification is a necessity, both to find suitable placements for the steady flow of confiscated, wild- caught animals, and to enable the existing zoo stock to be used to the best advantage – as Dr Geissmann points out, misidentification and consequent hybridisation are serious problems in zoos. (Surveys of European and North American zoo gibbons in the early 1980s found that over 4% were definitely hybrids, and the real total would undoubtedly be considerably higher.) So the present article – apart from its intrinsic zoological interest – is important as an aid to practical conservation. For reasons of cost it was impossible to include colour photos of infant, juvenile and subadult gibbons, whose appearance often differs considerably from that of their elders. Should funding become available, Dr Geissmann hopes to be able to publish a more comprehensive colour guide to the gibbons at some future date; he would be very glad to hear from anyone who might be able to help with this. Coincidentally, it was a letter to me from Thomas Geissmann which triggered the changes to I.Z.N.’s presentation which I introduced at the beginning of 1995. The indexes to contributors, books reviewed and general subject-matter, which will in future be a regular feature of the last issue of each year, form a part of the same process. I hope readers will find them useful, as I myself am already starting to do. Ideally, I would like to issue similar indexes to earlier volumes; but realism compels me to admit that I am unlikely ever to do so unaided. The work is very labourintensive, and I have begun to appreciate for the first time why indexers regard their trade as one of the skilled professions! But should any readers with time on their hands fancy taking on the task of indexing one or more earlier volumes, I would be extremely grateful for their help... Nicholas Gould 466 International Zoo News Vol. 42, No. 8 (1995), pp. 467-501 GIBBON SYSTEMATICS AND SPECIES IDENTIFICATION BY THOMAS GEISSMANN [This paper is a revised and much enlarged version of an article which was originally published in German in Zeitschrift des Kölner Zoo Vol.37, No. 2 (1994), pp. 65–78.] Abstract A study of wild and captive gibbons and museum specimens, and a survey of the literature suggests that gibbons (genus Hylobates) include at least 11, possibly 12 species, which form 4 distinct groups (subgenera Hylobates, Bunopithecus, Nomascus, and Symphalangus): These are the 44-chromosome gibbons (including the Hylobates lar group and H. klossii: 5 species); the hoolock (H. hoolock, 1 species); the H. concolor group (3, possibly 4 species); and the siamang (H. syndactylus, 1 species). A key for the identification of adult gibbons based on visual characteristics is presented, together with colour photographs and distribution maps of all recognised species (11). In addition, diagnostic vocal characteristics of all species are described and illustrated with sonagrams. Introduction The gibbons, or lesser apes (genus Hylobates), are a relatively small and uniform group of primates. One might assume that the systematic relationships within this group were relatively simple and easily re- solved. This does not appear to be the case, however. Although several revisions of gibbon systematics have been published (e.g. Groves, 1972; Marshall and Sugardjito, 1986; Pocock, 1927) and various scenarios have been proposed to describe the radiation of this group (e.g. Chivers, 1977; Groves, 1993; Haimoff et al., 1982), the phylogenetic relationships even among the main divisions of the gibbons are unclear (see below). Nevertheless, research on gibbons during recent years has considerably increased our knowledge on these apes. For instance, a number of field studies have been devoted to social structure and ecology of most gibbon species (review in Leighton, 1987). The occurrence of hybrid zones between some gibbon species are relatively recent discoveries of considerable scientific interest for gibbon systematics (e.g. Brockelman and Gittins, 1984; Mather, 1992). Marshall and Marshall (1976) systematically described, and collected tape-recordings of, the territorial songs of various gibbon species in the wild and demonstrated their importance for species identification. That publication stimulated a large number of additional studies on gibbon vocalisation whose results are of considerable value for gibbon systematics (e.g. Geissmann, 1993; Haimoff et al. 1982, 1984; Marshall et al., 1986; Mitani, 1987). 467 Today, gibbons may be considered one of the best studied groups of primates. Many results of the gibbon research from the last 20 years are, however, not available to the non-specialist. These findings have usually been published in hardly-accessible scientific reports and theses, and most of them seem to be very reluctant to find their way into more popular text books and teaching books. For instance, the siamang is often being referred to a distinct genus (Symphalangus), although other gibbon subgenera (such as Nomascus or Bunopithecus) should also be raised to genus rank if Symphalangus were recognised as a genus. The Kloss gibbon (H. klossii) – although not closely related to the siamang – is still occasionally referred to as ‚dwarf siamang’ or Symphalangus klossii, and species such as Müller’s gibbon (H. muelleri) and pileated gibbon (H. pileatus) are often ignored or listed as subspecies of the lar gibbon (H. lar) (e.g. Berger and Tylinek, 1984). The identification of the various gibbon forms often appears to pose an even major problem, irrespective of the nomenclature adopted. A reliable identification of some gibbon species and subspecies based solely on fur coloration may not be feasible even for the specialist. In such cases, the analysis of vocal characteristics almost always resolves the uncertainty, at least when species identification is required. Unfortunately, it may be too late for a species diagnosis in the proper sense for many zoo gibbons: While visiting European and American zoos, I frequently met hybrid gibbons. In many cases, the owners did not know that their ‘Javan gibbons,’ ‘lar gibbons’ or ‘hoolocks’ were, in reality, mixed pairs or hybrid offspring of such pairs. Believing that they had been breeding pure taxa, some institutions had for years sent their surplus gibbon offspring as pure species to other gibbon holders, and, by doing so, had unknowingly helped spreading the species mixture in the captive population even further. It is clear,then, that a serious lack of information exists. In the present report I would like to summarise current views on gibbon evolution and systematics and provide an identification key for all currently recognised species. Colour photographs of all species and a description of their songs are presented as an additional aid for species identification. Some other topics which would also be relevant in this context, such as the identification of subspecies and hybrid gibbons, and colour changes in young and maturing gibbons, cannot be covered here. Such a comprehensive treatment would exceed the space limitations of a journal article and must be reserved for future publications. Gibbon Systematics It is generally accepted that gibbons, great apes and humans together form the monophyletic group Hominoidea (Groves, 1989). It has also been widely accepted in recent years that the gibbons constitute the sister group to the great apes and humans (Fig. 1), and show the most primitive characteristics within the Hominoidea (Fleagle, 1984). This view is sup- ported by results from comparative studies of a wide array of morpholo- gical (Biegert, 1973; Remane, 1921; Sawalischin, 1911; Schultz, 1933, 1973; Wislocki, 1929, 1932), physiological (Hellekant et al., 1990), cytogenetic (Wienberg and Stanyon, 1987) and molecular data (Darga et al., 1973, 1984; Dene et al., 1976; Doolittle et al., 1971; Felsenstein, 1987; Goldman et al., 1987; Sarich and Cronin, 1976; Sibley and Ahlquist, 1984, 1987). 468 Wet-nosed primates Strepsirhini Tarsiers Tarsius New World monkeys Platyrrhini Apes and humans Old World monkeys Cercopithecoidea (Hominoidea) (Catarrhini) Old World Gibbons Hylobates primates Orang-utans Pongo Gorillas Gorilla Chimpanzees Pan Humans Homo Fig. 1. Systematic position of the gibbons within the primate order. Groves (1972) lar group hoolock klossii syndactylus concolor group Chivers (1977) Haimoff et al.

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